Incidence and severity of rice diseases and insect pests in relation

to climate change

Mainul Haq1, M A Taher Mia2, M F Rabbi1 and M A Ali21Entomology and 2Plant Pathology Division

Bangladesh Rice research Institute, Gazipur

International Symposium on Climate Change and Food Security in South Asia

25-30 August 2008

Dhaka, Bangladesh

Introduction

increase average water vapour and evaporationincrease precipitation in high-latitude regionschange in storm patterns (Emanuel 2005; Webster et al. 2005), which could influence the global movement of pests, especially pathogens (Brown and Hovmoller 2002)

Increased concentration of atmospheric CO2 is the key factor for global warming. IPCC predicted that global mean temperature would rise between 0.9 to 3.5ºC by the year 2100 (IPCC 2001). Global warming may-

Introduction

Prevailing environmental factors play vital role on incidence and severity of pests In Bangladesh, out of 32 diseases and 175 insect pests reported to occur on rice, 10 diseases and 20 insect pests have the potentiality to cause economic damage to the crop and considered as major Status of pests is dynamic Under changed climatic condition, cropping pattern & intensity may be changed and to cope up the situation new varieties may also be released, which might have either positive or negative impact on pests

Introduction

Climatic changes i.e. rise in temperature might also have a negative effect on delicate natural enemies such as hymenopteran parasitoides and small predators

Present paper deals with

-the change occurred on the status of pests over the last couple of decades

-predicted change on the status of pests and

-approaches to mitigate the problems

Status of insect pests over the years

Incidence pattern of insect pests

A Pennsylvanian light trap placed in a corner of the BRRI farm was operated dusk to dawn every day from January 1981 to December 2006.

Total number of individual pest trapped in a year (January 1 to December 31) was considered as the severity of that pest in that particular year.

Incidence pattern of five major insect pests viz., brown plant hopper, leaf roller, caseworm, green leaf hopper and stem borer over the last 25 years are presented here.

Brown planthopper

y = 857.17x + 10978R2 = 0.1841

y = 0.0114x + 30.446R2 = 0.0592

y = 0.0535x + 20.404R2 = 0.5473

0

10000

20000

30000

40000

50000

60000

70000

1981 1986 1991 1996 2001 2006

Year

Popu

latio

n

0

5

10

15

20

25

30

35

tem

p

BPHM axiM iniLinear (BPH)Linear (M axi)Linear (M ini)

Fig. 3a. Brown planthopper population at Gazipur over the year 1981-06

Green leafhopper

y = 0.0114x + 30.446R2 = 0.0592

y = 0.0535x + 20.404R2 = 0.5473

y = 174.9x + 24277R2 = 0.0059

010000

2000030000

4000050000

6000070000

80000

1981 1986 1991 1996 2001 2006

Year

Popu

latio

n

0

5

10

15

20

25

30

35

trm

p

GLH

M axi

M ini

GLH

M axi

M ini

Linear (M axi)

Linear (M ini)

Linear (M axi)

Linear (M ini)

Linear (GLH)

Linear (GLH)

Fig. 3b. Green leaf hopper population at Gazipur over the year 1981-06

Caseworm

y = -54.638x + 2353.7R2 = 0.0706

y = 0.0114x + 30.446R2 = 0.0592

y = 0.0535x + 20.404R2 = 0.5473

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

1981 1986 1991 1996 2001 2006

Year

Popu

latio

n

0

5

10

15

20

25

30

35

Tem

pera

ture M axi

M iniCWLinear (CW)Linear (M axi)Linear (M ini)

Fig. 3c. Caseworm population at Gazipur over the year 1981-06

Leaf roller

y = 0.0114x + 7.8366R2 = 0.0592

y = 0.0535x - 85.487R2 = 0.5473

y = -114.52x + 229549R2 = 0.4185

0

1000

2000

3000

4000

5000

6000

1981 1986 1991 1996 2001 2006 2011

Year

Inse

ct p

opu

0

5

10

15

20

25

30

35

Tem

p

LR

M axi

M ini

Linear(M axi)Linear(M ini)

Fig. 3d. Leaf roller population at Gazipur over the year 1981-06

Stem borer

y = -843.86x + 21952R2 = 0.2938

y = 0.0114x + 30.446R2 = 0.0592

y = 0.0535x + 20.404R2 = 0.5473

0

10000

20000

30000

40000

50000

6000019

81

1986

1991

1996

2001

2006

Year

Pop

ulat

ion

0

510

15

20

2530

35

tem

p

Stemborer

Maxi

Mini

Linear(Stemborer)Linear(Maxi)Linear (Mini)

Fig. 3e. Stem borer population at Gazipur over the year 1981-06

0

20000

40000

60000

80000

100000

120000

Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec

Month

Popu

latio

n (n

o.)

GLH BPH

Fig.4a. Monthly incidence pattern of GLH and BPH at Gazipur (1998 to 2007)

1

10

100

1000

10000

100000

Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec

Monyh

Popu

latio

n (n

o.)

LR SB CW

Fig.4b. Monthly incidence pattern of LR, SB and CW at Gazipur (1998 to 2007)

Predicted change in population of insect pest

Reproductive biology of an insect pest may be affected both positively and negatively which ultimately affect its population build-up (Chapman and Reiss, 1995)

Increase in temperature may be detrimental to delicate natural enemies specially the small parasitoids and may affect natural enemy-pest relationship

Brown planthopper is 17 times more tolerant to 400c than its predator Cyrtorrhynus lividipennis but wolf spider pardosa pseudoannulata was more tolerant to 400c

Predicted change in population of insect pest

Changes in temperature may interact with the cropping pattern affecting arthropod diversity in a region. Moreover, rise in temperature in winter may help to continue the life cycle of some pest without disruption in Boro season

Status of diseases over the years

Changes observed in sheath blight disease status

Sheath blight (Rhizoctonia solani) disease has occurred in Bangladesh from a long time as a minor disease (Talukder 1968) Presently, it is one of the most devastating disease in rice (Miah et al. 1985). High temperature and high relative humidity (RH) is very much conducive for rapid proliferation of this diseaseReplacement of indigenous varieties with thick canopy, high N-responsive ones along with climate change probably influenced the disease and changed its status

Sheath blight disease symptom

Affected sheaths Affected leaves

Change in Sheath blight incidence over years

0

5

10

15

20

25

30

1976-85 19886-95 1996-05

Period

Inci

denc

e (%

)

Fig. 1. Incidence pattern of sheath blight disease during 1976-2005

Fig. 2. Average of daily minimum temperature (0C) during last three decades at Comilla

5.00

10.00

15.00

20.00

25.00

30.00

1 31 61 91 121 151 181 211 241 271 301 331 361

Days of the years

Tem

p 0C

1981-90 1991-00 2001-05

J F M A M J J A S O N D

Blast disease -symptoms

Change in blast disease incidence

First repot in the Indian sub-continent in 1913 (Padmanabhan 1965).

In Bangladesh blast was relatively unimportant in late sixties and early seventies (Anon 1977).

In 1980 and 1990 outbreaks of blast observed in Boro season. (Miah et al. 1980; Shahjahanet al. 1991).

Probable reasons of blast outbreak in 1990

Source: Shahjahan et al 1991

Change in blast disease incidence

Northern parts of the country were free from blast but recently neck blast has been found to occur in T. Aman and Boro crops in Rajshahi, Joypurhat, Sirajgonj and Bogra districts

Presently this disease is almost wide spread in the country with medium to high incidence in Boro and T. Aman seasons

Bakanae disease-Symptom

Change in bakanae disease incidence

Bakanae (Fusarium moniliforme) disease of rice used to occur mostly in Aus season and was of little importance in Boro crop

Since 2000 it has become a big concern for Bororice especially in single Boro areas

Rise in minimum temperature during winter might have increased the incidence of bakanae in Boroseason

Ufra disease-Symptom

Change in ufra disease incidence

Ufra disease (Ditylenchus angustus) was reported for the first time in deep-water ecosystem (Butler 1913)

Gradually this disease has spread both in rainfedand irrigated ecosystem

It covered in 18 districts of Bangladesh in 1990s

After 2000, area under this disease is gradually shrinking

Bacterial leaf streak -symptom

Change in Bacterial leaf streak

Recently (Boro 2008) bacterial leaf streak (X. campestris pv oryzicola) emerged as an alarming proportion especially in south and southwest parts of the country might be due to varieties and environmental factors especially rain and storm

Predicted climate change and Disease severity

Predicted change in plant due to global warming

According to Pritchard et al (1999), elevated CO2 level tend to result in

-increased leaf area (LA); leaf thickness

-higher number of leaves

Life span of rice varieties will be shortened

Minimum temperature in winter may rise further increased severity of sheath blight & stem rot is most likely

Predicted change in plant due to global warming

Increased plant density will tend to increase leaf surface wetness and leaf surface wetness duration make infection by foliar pathogens more likely (Harvell et al. 2002), especially by Pyriculariagrisea, causing blast disease of rice.

Increase in temperature would aggravate blast disease in winter but may have a negative impact in T. aman.

There is possibility of increased incidence and severity of blast in northern parts of Bangladesh.

Predicted change in abiotic factors

Increases in UV-B radiation is likely due to depletion of ozone layer resulting-

increased production of secondary plant metabolites that might change the host-pathogen relationship and also the status of individual pest (Renger et al. 1989; Cladwell et al. 1989) and also

increased susceptibility of rice to blast disease (Olszyk and Ingram 1993).

Predicted change in abiotic factors

Drought conditions predispose rice plants to Bipolaris oryzae

Possibility of increased severity of this disease is high

Intensity and severity of drought may be increased

Approaches to mitigate the predicted problems

Survey & monitoring of diseases and insect pests

Monitoring pathogen population at regular interval to determine if there is any change

Strengthen screening programme

Use of molecular tools

Extensive search for thermophilic BCA

Use already developed management practices until these remain effective

Manipulation of cultural practices